Back to EveryPatent.com
United States Patent |
5,526,458
|
Hochgraf
|
June 11, 1996
|
Vision system with fiber optic plate to detilt oblique images
Abstract
A light directing element (22) used in a Scheimpflug system (10, 12, 14,
16, 18) includes an array of closely packed optical fibers (40) formed as
a plate (34) having essentially parallel entrance and exit sides (36, 38),
the axis (44) of each fiber of the array being essentially perpendicular
to the exit side and at a first oblique angle (.gamma.) to a normal to the
entrance side, the normal to the entrance side being at a second oblique
angle (.alpha.) to the first axis; so that, each fiber receives light from
the first optical system, each fiber being curved between the entrance and
exit sides. Oblique objects can be viewed in real time using electronic
detectors (28-32) which receive light emitted from the exit side. Objects
with topographical features (11) may be viewed by providing the entrance
side with an optically conjugate surface of topography (23).
Inventors:
|
Hochgraf; Neil A. (Rochester, NY)
|
Assignee:
|
Eastman Kodak Company (Rochester, NY)
|
Appl. No.:
|
250149 |
Filed:
|
May 27, 1994 |
Current U.S. Class: |
385/120; 250/227.28 |
Intern'l Class: |
G02B 006/08 |
Field of Search: |
385/120
250/227.11,227.23,227.26,227.28,227.29
|
References Cited
U.S. Patent Documents
4099833 | Jul., 1978 | Tosswill | 385/120.
|
4492424 | Jan., 1985 | Clegg | 385/120.
|
4867530 | Sep., 1989 | Sedlmayr | 385/120.
|
4943157 | Jul., 1990 | Reding | 356/1.
|
5010241 | Apr., 1991 | Butterworth | 235/462.
|
5032023 | Jul., 1991 | Schneiter | 356/1.
|
5102226 | Apr., 1992 | Yoshimura et al. | 356/376.
|
5164603 | Nov., 1992 | Hartman et al. | 250/272.
|
5347122 | Sep., 1994 | Ansorge et al. | 385/120.
|
Foreign Patent Documents |
164527 | Nov., 1905 | DE.
| |
3200148 | Oct., 1982 | DE | 385/120.
|
0140673 | Nov., 1981 | JP | 385/120.
|
Primary Examiner: Bovernick; Rodney B.
Assistant Examiner: Wise; Robert E.
Attorney, Agent or Firm: Snee, III; Charles E.
Claims
Having thus described my invention in sufficient detail to enable those
skilled in the art to make and use it, I claim as new and desire to secure
Letters Patent for:
1. A vision system, comprising:
a first optical system (12) for receiving light reflected from an object
plane (10) to be viewed, the first optical system having a first axis
(14), the first optical system defining a system plane (16) transverse to
the first axis;
a light directing member (22) for receiving light from the first optical
system, the light directing member including an array of closely packed
optical fibers (40) formed as a plate (34) having essentially parallel
entrance and exit sides (36,38), a central axis (44) of each fiber of the
array being (i) essentially perpendicular to the exit side and (ii) at a
first oblique angle (.gamma.) to a normal (42) to the entrance side, the
normal to the entrance side being at a second oblique angle or incidence
(.alpha.) to the first axis, the angles (.gamma., .alpha.) being selected
so that light from the first optical system is refracted into the
acceptance cone of each fiber, each fiber being curved between the
entrance and exit sides and the acceptance cone being defined for each
fiber at a plane perpendicular to the central axis in a curved portion of
each fiber; and
a detector (28) for receiving light emitted from the exit side of the light
directing member and producing electrical signals in response to the
received light.
2. A vision system according to claim 1, wherein the detector includes a
CCD array and the light directing member forms a window in front of the
CCD array, each fiber being self focusing.
3. A vision system according to claim 1, wherein an object to be viewed
defines the object plane; the first optical system comprises a lens
defining the system plane; the entrance side of the light directing member
defines a first image plane; and the object plane, lens plane and first
image plane, when extended, intersect on a common line.
4. A vision system according to claim 1, further comprising a second
optical system (24) for relaying light from the light directing member to
the detector, the second optical system having a second axis (26)
essentially perpendicular to the exit side and the detector defining a
second image plane essentially perpendicular to the second axis.
5. A vision system to claim 1, wherein the detector includes a CCD array
and the light directing member forms a window in front of the CCD array,
each fiber being in near contact with a front surface of the array.
6. A light directing member (22) for receiving light along a first axis
(14) and emitting light along a second axis (26), comprising:
an array of closely packed optical fibers (40) formed as a plate (34)
having essentially parallel entrance and exit sides (36, 38), a central
axis (44) of each fiber of the array being essentially perpendicular to
the exit side (38) and at an oblique angle (.gamma.) to a normal (42) to
the entrance side 36, so that each fiber can receive light along a first
axis at an angle of incidence (.alpha.) at the entrance side, the angle
(.gamma.) being selected so that in use of the member at angle (.alpha.),
light along the first axis is refracted into an acceptance cone for each
fiber and each fiber can emit light along the central, second axis at the
exit side, each fiber being curved between the entrance and exit sides and
the acceptance cone being defined for each fiber at a plane perpendicular
to the central axis in a curved portion of each fiber.
7. A method for viewing an object, comprising the steps of:
illuminating the object, the object defining an object plane (10);
relaying light reflected, scattered or diffracted from the object through a
first optical system having a first optical axis (14);
receiving light from the first optical system at an entrance side (36) of
an array of closely packed optical fibers (40) formed as a plate (34)
having essentially parallel entrance and exit sides (36, 38), a central
axis (44) of each fiber of the array being essentially perpendicular to
the exit side and at an oblique angle (.gamma.) to a normal (42) to the
entrance side, the normal to the entrance side being at a second oblique
angle of incidence (.alpha.) to the first optical axis, the angles
(.gamma., .alpha.) being selected so that light along the first axis is
refracted into an entrance cone for each fiber and emitted from the exit
side along the central axis, each fiber being curved between the entrance
and exit sides and the acceptance cone being defined for each fiber at a
plane perpendicular to the central axis within the curved portion of each
fiber;
relaying light emitted from the exit side to a detector (28) for received
light; and
producing with the detector electrical signals in response to the received
light.
8. A method according to claim 7, wherein the first optical system
comprises a lens (12) defining a lens plane (16) transverse to the first
axis; and the entrance side defines a first image plane (18), further
comprising the steps of:
orienting the object plane, lens plane and first image plane so that the
planes, when extended, intersect on a common line.
9. A method according to claim 7, wherein the step of relaying light
emitted comprises a step of passing the emitted light through a second
optical system having a second axis essentially perpendicular to the exit
side; and the detector defines a second image plane; further comprising
the step of orienting the second image plane essentially perpendicular to
the second axis.
10. A method of making a light directing member, comprising the steps of:
forming a closely packed bundle of optical fibers, the bundle having an
axis and first and second ends;
holding the first end of the bundle to prevent substantial relative
movement of the fibers at the first end;
holding the second end of the bundle to prevent substantial relative
movement of the fibers at the second end;
relatively moving the first and second ends of the bundle transverse to the
axis to doubly curve the optical fibers within the bundle; and
fuzing the bundle to maintain the double curve.
11. A method according to claim 10, further comprising the step of:
transversely cutting the bundle near the center of the double curve to form
two light directing members, each comprising an array of closely packed
optical fibers formed as a plate having essentially parallel entrance and
exit sides, the axis of each fiber of the array being essentially
perpendicular to the exit side and at an oblique angle to a normal to the
entrance side, so that each fiber can receive light along a first axis and
emits light along a second axis, each fiber being curved between the
entrance and exit sides.
12. A method according to claim 11, further comprising the step of:
polishing the ends of the fibers at both ends of the bundle.
13. A method according to claim 11, further comprising the step of:
forming the entrance side to a shape optically conjugate to a shape of an
object to be viewed.
14. A method of making a light directing member, comprising the steps of:
forming a closely packed bundle of optical fibers, the bundle having an
axis and first and second ends;
holding the first end of the bundle to prevent substantial relative
movement of the fibers at the first end;
frictionally engaging a plate with the ends of the fibers at the second
end;
relatively moving the first end of the bundle and the plate transverse to
the axis to singly curve the optical fibers within the bundle; and
fuzing the bundle to maintain the single curve, thereby forming a light
directing member including an array of closely packed optical fibers
formed as a plate having essentially parallel entrance and exit sides, a
central axis of each fiber of the array being (i) essentially
perpendicular to the exit side and (ii) at a first oblique angle to a
normal to the entrance side, each fiber being curved between the entrance
and exit sides.
15. A method according to claim 14, further comprising the step of:
polishing the ends of the fibers at both ends of the bundle.
16. A method according to claim 14, further comprising the step of:
forming the entrance side to a shape optically conjugate to a shape of an
object to be viewed.
Description
TECHNICAL FIELD
The invention relates to electronic vision systems. More particularly, the
invention concerns machine vision systems for viewing objects at oblique
angles, the light reflected from the object being redirected into a path
essentially perpendicular to the surface of an image plane.
BACKGROUND ART
Preferably, the plane of an object to be photographed or viewed should be
essentially perpendicular to the optical axis of the camera or viewing
system; and the image plane should be perpendicular to the same optical
axis. In a variety of applications, though, this preferred geometry can be
maintained only with great difficulty and inconvenience. Examples would be
photographing tall buildings from ground level or viewing objects from a
small oblique angle to the object plane, where the object plane is tilted
considerably relative to both the optical axis and the image plane.
Acceptable focus of all parts of the image may not be attainable.
An early solution to this type of problem is found in German Patent
164,527, granted to Theodor Scheimpflug, who discovered that well-focused
images could be obtained under such circumstances if the object and image
planes were made to intersect with plane of the optical system (lens) on a
common straight line. The general arrangement of a Scheimpflug viewing
system is shown in FIG. 1. An obliquely tilted object plane 10 is viewed
through a first optical system such as a lens 12, which has an axis 14
forming an oblique angle with object plane 10. The plane 16 of lens 12 is
essentially perpendicular to axis 14 in the illustrated system but could
also be at an oblique angle. An image plane 18 forms an angle of incidence
.alpha. between axis 14 and a normal to the image plane. Scheimpflug
taught that a good image could be formed at image plane 18, provided that
object plane 10, lens plane 16 and image plane 18 intersect along a common
line 20. Thus, photographic film placed at image plane 18 could be exposed
to produce a good image of an object at plane 10. Photographic film is
especially suited for use in Scheimpflug systems since film can be made
large enough to accommodate most images and will capture images using
incident light at very large angles of incidence approaching parallel to
the surface of the film.
In various more modem vision systems, however, real time observation of an
object is desired, such as the condition of a product or machine pan
during performance of an industrial process. Often, access to the object
to be viewed is rather severely limited, which may require use of viewing
angles of only several degrees from the plane defined by the object. While
a Scheimpflug system can be applied in such situations with acceptably
good results when conventional photographic film is exposed at the to
image plane, difficulties arise when real time measurements are desired
using an electronic detector such as a CCD array or the like, including
camera tubes. Such detectors typically are rather small, making it
difficult to capture an entire image of the object. In addition, such
detectors rather typically are recessed within a camera housing or an
integrated circuit housing, thus requiring a rather small angle of
incidence (45.degree. maximum) or an unusually large, very expensive
detector to provide sufficient area to receive light from the object.
Furthermore, optical anti-reflection coatings commonly used on such
detectors are generally designed for nearly normal incident light, not
very oblique light such as would be received in systems similar to that of
FIG. 1.
Thus, a need has existed for a simple, inexpensive device for redirecting
light received from the object at the image plane in a Scheimpflug type
system; so that the light can be relayed to an electronic detector along
an axis more nearly normal to the surface of the detector.
SUMMARY OF THE INVENTION
The invention is defined by the appended claims. In one embodiment, a
vision system includes a first optical system for receiving light
reflected, scattered or diffracted from an object to be viewed, the first
optical system having a first axis. A light directing member according to
the invention is provided for receiving light from the first optical
system. The light directing member includes an array of closely packed
optical fibers formed as a plate having essentially parallel entrance and
exit sides, the axis of each fiber of the array being (i) essentially
perpendicular to the exit side but (ii) at a first oblique angle to a
normal to the entrance side. The normal to the entrance side is set at a
second oblique angle to the first axis; so that, each fiber receives light
from the first optical system. Between the entrance and exit sides, each
fiber is gently curved. An electronic detector is positioned for receiving
light emitted from the exit side of the light directing member. The
detector produces electrical signals in response to the received light.
The light directing member may form a window directly in front of the
detector, without any intervening relay lenses.
Preferably, the object to be viewed defines an object plane; the first
optical system comprises a lens defining a lens plane transverse to the
first axis; the entrance side defines a first image plane; and the object
plane, lens plane and first image plane, when extended, intersect on a
common line, to satisfy the Scheimpflug conditions. A second optical
system may be provided for relaying light from the light directing member
to the detector, the second optical system having a second axis
essentially perpendicular to the exit side and the detector defining a
second image plane essentially perpendicular to the second axis. For
efficient transmission of light through the light directing member, the
light received from the first optical system at the entrance side
preferably is refracted initially by each fiber into an acceptance cone
defined for the fiber at a plane perpendicular to the axis of the curved
portion of the fiber. The invention also comprises a method of viewing an
object using such a light directing member.
The light directing member may be made in accordance with the invention by
forming a closely packed bundle of optical fibers, the bundle having an
axis and first and second ends; holding the first end of the bundle to
prevent substantial relative movement of the fibers at the first end;
holding the second end of the bundle to prevent substantial relative
movement of the fibers at the second end; relatively moving the first and
second ends of the bundle transverse to the axis to doubly carve the
optical fibers within the bundle; and finally fuzing or curing the bundle
to maintain the double curve. By transversely cutting the bundle near the
center of the double curve, two light directing members can be formed,
each comprising an array of closely packed optical fibers formed as a
plate having essentially parallel entrance and exit sides, the axis of
each fiber of the array being essentially perpendicular to the exit side
and at an oblique angle to a normal to the entrance side, so that each
fiber receives light along the first axis and emits light along the second
axis, each fiber being curved between the entrance and exit sides.
An alternative method of making the light directing member comprises
forming a closely packed bundle of optical fibers, the bundle having an
axis and first and second ends; holding the first end of the bundle to
prevent substantial relative movement of the fibers at the first end;
frictionally engaging a plate with the ends of the fibers at the second
end; relatively moving the first end of the bundle and the plate
transverse to the axis to singly curve the optical fibers within the
bundle; and finally fuzing or curing the bundle to maintain the single
curve. By suitably polishing the ends of the fibers at both ends of the
bundle, the light directing member is completed.
The invention provides numerous advantages. Real time viewing of objects
whose object plane is quite oblique to the available viewing axis is
achieved using modern electronic detectors which otherwise would not be
well suited for such applications. The light directing member of the
invention can be made using a small volume of conventional fiber optic
elements and a simple assembly method. The member can be light weight and
thin and is easily mounted like a lens. The optimum position within a
given optical system is easily determined.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other features and advantages of the invention will be
apparent from the following more particular description of the preferred
embodiments of the invention, as illustrated in the accompanying drawings.
FIG. 1 illustrates schematically a prior art imaging system of the general
type taught by Scheimpflug.
FIG. 2 illustrates a vision system according to the present invention.
FIG. 3 illustrates the unique light directing member according to the
invention.
FIG. 4 illustrates a fragmentary portion, partially in section and
partially broken away, of the light directing member of FIG. 3 and
indicates the geometric relationships of the various elements of the
member.
FIG. 5 illustrates an alternative application of the light directing
member.
FIG. 6 and FIG. 7 illustrate schematically alternative methods for making
the light directing member.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following is a detailed description of the preferred embodiments of the
invention, reference being made to the drawings in which the same
reference numerals identify the same elements of structure in each of the
several Figures.
FIG. 2 illustrates a vision system suitable for a wide variety of
applications in which an object can be viewed conveniently only from a
rather small oblique angle. A light directing member 22 according to the
invention is positioned at image plane 18 of a Scheimpflug type imaging
system. Object plane 10 is illuminated by suitable means not illustrated.
Member 22 causes the light from lens 12 to be redirected to a second
optical system which may comprise a lens 24 with an axis 26 essentially
perpendicular to member 22. Light passing through lens 24 falls
essentially normally on a conventional electronic detector 28, such as a
CCD array. The second optical system may be configured to magnify or
reduce the size of the image to detector 28. In the familiar manner,
detector 28 produces electrical signals in response to the received light
and passes the signals over a suitable cable 30 to a suitable display 32
which may comprise a computer-based image processor. Thus, as the
conditions at object plane 10 change, they can be observed and processed
in real time by display 32. Alternatively, member 22, lens 24 and detector
28 can be set at angles to axis 26 which will establish a second
Scheimpflug system. The benefit of such a second Scheimpflug system would
be to reduce distortion of the image at detector 28.
As seen in FIGS. 3 and 4, light directing member 22 has the form of a plate
34 with an essentially planar light entrance side 36 and, essentially
parallel to entrance side 36, an essentially planar light exit side 38. To
satisfy the Scheimpflug conditions, entrance side 36 should be essentially
coplanar with image plane 18. By "essentially" planar or coplanar or
parallel is meant that the sides of member 22 may deviate somewhat from
planarity or coplanarity or parallelism, without departing from the scope
of the invention, to the extent that the image can be tolerated to be out
of focus. For example, an object having a surface 11 with topographical
features as shown in phantom lines in FIG. 2 may be imaged in accordance
with the invention by grinding or otherwise treating member 22 to provide
at entrance side 36 an optically conjugate surface 23 for the
magnification of lens 12, as also shown in phantom lines in FIG. 2, with
an obliquity which meets the Scheimpflug conditions.
Member 22 is formed from an array of closely packed, fuzed optical fibers
40, such as commercially available fibers preferably having diameters in
the 3 to 4 micron range, which will provide approximately 50 line pairs
per millimeter resolution. Thus, resolution at the detector when using
member 22 is good, particularly when lens 12 enlarges the image at side 36
and lens 24 reduces the image at the detector. As shown in FIG. 4, each
fiber 40 comprises a central core 41 surrounded by a layer of cladding 43
in the familiar manner. Among the fibers, a conventional bonding material
45 such as a resin or low melting point glass falls the interstices and,
when cured or fuzed, holds the array together. Such resolution is better
than most CCD detectors, which typically have pixel sizes of about 7 to 14
microns in width. Member 22 may have any convenient geometry on its
perimeter, such as round or rectangular; so long as sufficient area is
provided on entrance side 36 for receiving the light imaged by lens 12.
The area of member 22 need only equal that of the oblique image and
usually must be rectangular. Large image area at side 36 should ensure
that the object can be seen better in its spatial context.
As seen best in FIG. 4, a normal 42 to entrance side 36 forms an oblique
angle .gamma. with a central, longitudinal axis 44 of each fiber; but axis
44 is essentially perpendicular to exit side 38 which preferably is
essentially normal to axis 26, as shown in FIG. 2. The ends of the fibers
at sides 36, 38 preferably should be polished to be essentially coplanar
at the respective surfaces. Typically, angle .gamma. should be in the
range of 30 to 40.degree. toward axis 44 for modem high index glasses of
the types used in conventional optical fibers. Between sides 36 and 38,
each fiber curves gently and for most applications, all fibers will have
the same curvature. The fibers all curve in the same direction, rather
like stalks of wheat bent by the wind to one side. A single curve within
the thickness of the plate is preferable; however, multiple or compound
curves may be used provided the curvatures are not too sharp. The overall
thickness t of member 22 is not critical but must be sufficient to permit
the fibers to be curved to the desired final position without unacceptable
light loss. For example, for a 30.degree. tilt of the fibers and a bend
radius of about 8.0 mm, a plate thickness of about 4.0 mm would be
sufficient. Of course, the thicker the plate, the greater will be the cost
of the fibers. Short bend radii of the fibers increase the cone angle of
exiting light, even if the entering light was parallel and right down the
axis of the fiber at the entrance side.
For best efficiency of transmission of light along each fiber, angle of
incidence .alpha. between normal 42 and optical axis 14 should be held
within a range, giving due account to the indices of refraction of the
materials of the core and cladding of the fibers, to provide a suitable
angle of refraction .beta. within each fiber. That is, the light received
from the first optical system at entrance side 36 preferably should be
refracted initially by each fiber into an acceptance cone defined for the
fiber at a plane 46 perpendicular to axis 44 within the curved portion of
the fiber. When the light refracts from side 36 into such an acceptance
cone, even though the fibers are curved within element 22, the light
losses will be minimized and light will leave the fibers essentially
perpendicular to surface 38 as small, compact beams which ensure good
resolution. For optimum efficiency, the cone of the entering light should
be within the cone angle at which the fiber can efficiently receive and
transmit light. Preferably, the cone of the exiting light should be within
the f number subtended by the following relay optics, such as lens 24; so
that, the lens will be able to accept essentially all of the light from
the exit side. Angles of incidence .alpha. as high as 80.degree. to
89.degree. can be accommodated. The tilt angle .gamma. of the fibers for
very wide image field angles may be varied across the plate as necessary
to ensure that incident light will stay within the acceptance cone of the
fibers. Preferably, the light passing along fibers 40 should experience
several tens of reflections, to ensure a more uniform output at side 38
and just to fill the entrance pupil of any following relay optics, such as
lens 24. Due to the curve provided in fibers 40 in accordance with the
invention, angle of incidence .alpha. may be as large 80 to 85 degrees, so
that incident light just skims entrance side 36, yet good transmission
through element 22 to detector 28 would be expected.
Light directing element 22 may be provided before a second optical system
as shown in FIG. 2, or may be positioned directly in front of the
detector, in contact or near contact, as illustrated in FIG. 5. When a
second optical system is not necessary, a housing 48 may be provided for
detector 28 and a tube or barrel 50 may be included to recess and protect
the detector in the familiar manner. In this instance, member 22 may be
mounted directly within barrel 50 just in front of detector 28. Member 22
may be in contact with detector 28 or the light may be imaged onto the
detector by self-focusing optical fibers. The approach to use may be
readily determined to provide best resolution and to allow appropriate
clearance for any wiring or other features of the detector. A peripheral
notch 37 may be provided adjacent exit side 38 to facilitate wiring to the
detector.
FIGS. 6 and 7 illustrate schematically a pair of methods suitable for
making light directing element 22. A bundle 52 of closely packed optical
fibers is provided whose perimeter geometry is suitable for an intended
application. A first end of the bundle is held by a fixed clamp 54 to
prevent substantial relative movement of the fibers at the first end. The
second end of the bundle is held by a movable clamp 56, also to prevent
substantial relative movement of the fibers at the second end. The first
and second ends of the bundle are then moved relative to one another along
essentially parallel paths transverse to axis 44 to doubly curve the
optical fibers within the bundle, as shown in FIG. 6. Finally, the bundle
is fuzed or cured using conventional techniques, to maintain the double
curve. By transversely cutting the bundle along a cut line 58 near the
center of the double curve and polishing the both ends of each of the
severed parts of the bundle, two light directing members 22 are formed.
An alternative method of making light directing member 22 comprises forming
a closely packed bundle of optical fibers; holding a first end of the
bundle with a fixed clamp 60 to prevent substantial relative movement of
the fibers at the first end; frictionally engaging a movable plate 62 with
the ends of the fibers at a second end; relatively moving the first end of
the bundle and the plate transverse to axis 44 to singly curve the optical
fibers within the bundle; and finally fuzing or curing the bundle to
maintain the single curve. By suitably polishing the ends of the fibers at
both ends of the bundle, the light directing member is completed.
While my invention has been shown and described with reference to
particular embodiments thereof, those skilled in the an will understand
that other variations in form and detail may be made without departing
from the scope and spirit of my invention.
PARTS LIST
10 . . . object plane
11 . . . topographical features of object
12 . . . lens
14 . . . axis of lens 12
16 . . . plane of lens 12 transverse to 14
18 . . . image plane
20 . . . common line of intersection of 10, 16, 18
22 . . . light directing member according to invention
23 . . . optically conjugate surface
24 . . . lens
26 . . . axis of 24
28 . . . detector
30 . . . suitable conductor or cable
32 . . . video display or image processor
34 . . . plate
36 . . . light entrance side
37 . . . peripheral notch
38 . . . light exit side
40 . . . optical fibers
41 . . . core of 40
.gamma. . . . angle between normal 42 and axis of fiber 40
42 . . . normal to side 36
43 . . . cladding of 40
44 . . . axis of fiber 40
45 . . . bonding material
.alpha. . . . angle of incidence
.beta. . . . angle of refraction
46 . . . plane normal to axis 44
48 . . . housing for detector 28
50 . . . tube or barrel
52 . . . bundle of optical fibers 40
54 . . . fixed clamp
56 . . . movable clamp
58 . . . cut line
60 . . . fixed clamp
62 . . . movable frictionally engaged plate
Top